Ink compositions which remain erasable for an initial period have been proposed. In particular, ball-point pens employing erasable black ink compositions comprising rubber, a low boiling solvent, a black pigmenting material and a high boiling solvent [such as those described in Examples 1 and 2 and preferred range of Japanese Patent Application (OPI) No. 156731/79 which corresponds to U.S. Pat. No. 4,097,290 (Muller et al)] are known.
In brief, U.S. Pat. No. 4,097,290 to Muller et al teaches an erasable black ink composition for ball-point pens comprising rubber in an amount in the range of 22.5 to 26% by weight based on the total weight of the composition, a low boiling rubber solvent in an amount such that the weight ratio of the low boiling rubber solvent to the rubber is in the range of 1.04 to 1.19, a black pigment in an amount such that the weight ratio of the black pigment to the rubber is in the range of 0.65 to 0.89, and a high boiling solvent in an amount such that the weight ratio of the high boiling solvent to the black pigment is in the range of 1.5 to 1.53.
Ball-point pens using such inks are satisfactory in terms of erasability but are unsatisfactory in terms of writing properties. For example, they tend to be more or less scratchy because an insufficient amount of ink flows from the writing tip end. In addition, after a long period of use, they tend to provide extremely faint and non-uniform ink traces or may be completely clogged up even when a substantial amount of ink is still contained in the cartridge as shown in Comparative Examples 2 and 3 herein.